Signaling system and electromagnetic mechanism therefor



April 17; 1934. c BEACH 1,954,794

SIGNALING SYSTEM AND ELECTROMAGNETIC MECHANISM THEREFOR Filed July 16.1928' 2 Sheets-Sheet 2 To AC SUPPLY R 51a 1 L 3 /zz H/ K i m i 3/ fig IFv a n /l f 3/ FH 3/ 3/ PH 6 1:1 1 i 7 v 4 .9 5" a PH sf 3/ 1Q 1 by. I 4}Q 4 Fig. 7

INVENTOR Lal Patented Apr. 17, 1934 UNITED STATES SIGNALING SYSTEM ANDELECTROMAG NETIC MECHANISM THEREFOR Clarence E. Beach,Boston,. Mass,assignor to The Gamewell Company, Newton Upper Falls, Mass, acorporation of Massachusetts Application July 16, 1928, Serial No.293,068

13 Claims. (Cl. 175320) This invention relates to signaling systems andelectromagnetic mechanism therefor; and, more particularly, to means andmethods for conveniently and inexpensively rendering the electromagnetsused in'the series circuits of such systems and elsewhere, operable byalternating current in an efiicient, reliable and quiet manner.

Electromagnets intended for energization by alternating current haveheretofore been constructed in accordance with variousanethods,substantially all of which widely differ, in many details, from themethods employed in the construction of electromagnets intended forenergization by direct current under similar conditions and to eifectcorresponding results. Examples of such differences are found in the useof laminated cores with a view of reducing the losses incident to directapplication of alternating current to the energization ofelectromagnets; the use of so-called shading coils or their equivalents,with a view of reducing the chatter incident to such energization ofsuch magnets; and the use of a transformer with two independentsecondary windings connected through rectifying 'units with therespective ones of two windings of an electromagnet, with a view ofhastening the release of the armature upon interruption of the circuitwhich furnishes the exciting current for the primary of the transformer.However, all such previous expedients with which I am acquainted haveimpaired, to an objectionable extent, the net operating efiiciency ofthe electromagnets, as compared with that of magnets excited by-a directcurrent circuit; and the use of all of such previous expedients inseries circuits involving aggregate impedance far in excess of that ofany one magnet and any rectifying mechanism associated therewith, hasincurred objectionable characteristics well understood by those skilledin this art, certain of which will be hereinafter referred to in greaterdetail.

There has been an increasing tendency toward recognitiorrof thedesirability of utilizing alternating current for multi-circuittelegraph signaling systems such, for example, as municipal andinstitutional fire alarm systems. It is generally recognized that eachsuch system should be subdivided into a plurality of circuits which areindependent in such sense that, if impairments of insulation orso-called crosses affect two or more circuits, such faults will not bepermitted other circuit or if defects simultaneously effective on two ormore circuits could cause the disablement (by shunting out) of all orpart of the signal initiating stations of the affected circuits; whichdisablement is likely to result from such conditions where a pluralityof circuits are supplied from a single direct current source. With aview of safeguarding the situation indicated, it is customary to provideindependent groups of battery cells for the respective circuits, storagebatteries being ordinarily used for this purpose, and two groups ofcells are customarily provided for each such circuit so that one groupof cells may be working while the other group is being charged or beingheld in reserve after charge, as it has been found to be undesirable toconnect the source of charging current to any battery while a workingline is being supplied by it. Thus, it has been found that in amunicipal fire alarm'system of a city requiring say 100 circuits,supplied by an average of 30 working and 30 reserve battery cells percircuit, an aggregate on the order of 6,000 battery cells is needed, thecost of care and maintenance of which involves a very substantial sumand the conditions of operation of which are highly incincient ascompared with the storage and delivery of a like energy in a singlegroup of cells of such size as to provide an ampere hour capacitysufilcient to supply all of the circuits with alternat ing currentthrough a motor generator for a time as great as that which any onecircuit could be operated by both of the groups of the smaller cellswhich are associated therewith.

For economic reasons, it has been found undesirable and impracticable toutilize greatly increased electromotive forces or current intensities inthe conductors of many such systems, and it has been generallyrecognized that, for like reasons, the series type circuit must be used.In determining how great a line current strength should be employed in agiven series circuit, it is necessary to take into consideration thecomparatively small size of line conductors which are usually availablefor the required service, with the resultant high line resistance andsmall current carrying capacity. Correspondingly, in determining howgreat an electromotive force can be safely applied to a given signalingcircuit, it is necessary to take into consideration the continuousdependability of the effectiveness of the break gap of the contacts ofavailable signal transmitting mechanisms, as well as safety to those ofthe public using such signaling systems and that of those employed inconstructing and maintaining such systems.

In connection with the question of continuous dependability ofeffectiveness of insulation, it should be remembered that emergencysignaling service of-this character requires greater safeguarding inmany respects than is necessary in signaling systems such, for example,as commercial telegraph and telephone systems, in which both the senderand receiver of the message is familiar withthe normal operation of thesystem and may immediately ask for confirmatory repetition of allimportant messages, and in which messages are sent from all stationswith sufiicient frequency to insure timely disclosure of graduallydeveloping faults. In contrast with such commercial systems, anemergency signaling system, such as a municipal fire alarm telegraphsystem,'includes sending stations, individual ones of which may not beoperated to call the fire department for many months-perhaps one or moreyears,but, when needed to summon the fire department, failure of anysuch station is likely to result in loss of property of great value andto expose human beings to a likelihood of being maimed or killed.Furthermore, there are many signaling systems, of various kinds andtypes, operation of which by direct current is being continued onlybecause it has been impracti-' cable to so alter the instrumentsincluded therein as to adapt them to successful operation in connectionwith an alternating current source applied in accordance with prior artpractice, but which could otherwise be so operated more dependably,'eificiently, inexpensively and satisfactorily than they now are.

In emergency signaling systems, using circuits in which the sendingstations are serially connected, the importance of the problem ofavoiding a high line voltage is emphasized by the fact that although thepotential applied between the conductor leading to a given transmittingstation and the conductor leading'from that station to the next, isnormally of a negligible magnitude, because it merely represents thefall of potential at normal line current strength across the resistanceor impedance of the current path through that station,-the voltagebetween such conductors rises to a value as great as or exceeding thatof the current source supplying the circuit (depending upon the presenceand extent of inductance of magnet windings in the circuit) at timeswhen the circuit is interrupted at a given sending station for thepurpose of formulating a signal therefrom. It is therefore evident thatinsulation between the conductors leading to and from any sendingstation, although sufficient to avoid breakdown for an indefinitely longtime during which the mechanism of that station does not act to breakthe line circuit, may nevertheless be insufi'icient to prevent itsbreakdown when subjected to the added strain of station activity; and itis obvious that such breakdown will impair or destroy the eifectivenessof the sending station mechanism in so breaking the line circuit as tocause intended response of signaling instruments at a time wheneffectiveness is of utmost importance.

It is an important object of this invention to provide electromagneticstructure and associated means adapted for operation in an alternatingcurrent circuit more efiiciently, reliably and quietly than heretofore.

It is a further important object to provide structure and means havingthe aforesaid characteristics, which may be made and used in aninexpensive and convenient manner.

It is a. further object to providain electromagoeavsa netic structure,the characteristic of minimizing variations in the impedance offeredthereby incidental to movement of an associated armature toward or awayfrom the magnetic poles of such structure.

It is a further object to provide means and methods which can beconveniently and inexpensively applied, whereby electromagnets of thetype ordinarily utilized in direct current signaling circuits may besuited for use in an alternating current circuit.

With the aforesaid objects in view, this invention consists of the novelcombinations, arrangements of parts and methods hereinafter described intheir preferred embodiments, pointed out in the claims, and illustratedin the annexed drawings, in which Figure 1 is a diagrammaticrepresentation of a signaling system embodying one aspect of thisinvention;

Fig. 2 represents electrical connections of windings of an electromagnetfunctionally corresponding to those of the magnets of Fig. 1;

Fig. 3 shows magnet winding connections, corresponding to those of Fig.2, together with those of another aspect of this invention;

Figs. 4 and 5 are simplified diagrammatic representations of thearrangements of Figs. 2 and 3, respectively, indicating .the directionof magnet windings;

Fig. 6 is a diagram representing the characteristics of the magneticexcitation resultant from recurrent circuit closures through windings ofan electromagnet arranged in accordance with the preceding figures; and

Fig.- 7 is a diagrammatic representation of a circuit of alarmresponsive instruments, such as circuit L of Fig. 1.

A signaling system representative of commonly used types of municipalfire alarm systems is shown in Fig. 1. This system comprises threesocalled street" or transmitting station circuits S S and S each suitedfor inclusion therein of a plurality of transmitting stations, such asthe stations TS, one of which is symbolically represented in connectionwith each of said circuits; a so-called local or receiving instrumentcircuit L for controlling a plurality of receiving instruments suchasare ordinarily provided at the various fire houses or other alarmreceiving stations, one such receiving station being indicated at RS bya symbolic representation of a tower bell striker; and an automaticrepeater R, through the action of which signals originating at anytransmitting station in any one of the circuits S S or S will beautomatically retransmitted into the others of said circuits and intothe local circuit L, in a manner well understood by those skilled inthis art.

At each of the transmitting stations TS is shown the winding spools 311of a U-magnet, control of the signal transmitting contacts by whichmagnet is symbolically indicated in a manner representative of suchrelationship as is ordinarily established by the so-callednon-interference magnet in well known commercial types of what arecommonly termed perfect non-interference and succession fire alarmboxes. A cutout CO is indicated at each station TS to symbolicallyrepresent the automatic switch provided in the types of commercial firealarm transmitting stations in general use, for the purpose of shuntingout the windings of the non-interference magnet when the mechanism isinactive, the shunt of which cut-out is automatically broken uponinitiation of the operation of the transmitting mechanism and thereafterremains broken until such mechanism comes to rest. It should beunderstood that any desired number of additional transmitting stationsmay be correspondingly included in the circuits S S and S to meet theservice conditions.

In the interests of simplicity, the representation of the automaticrepeater R is confined to those parts which may be included in therespective circuits; but the structural characteristics of the partsshown are such as to suit them for embodiment in a repeater of the kindindicated in U. S. Patent No. 1,613,018, dated January 4, 1927, toEdward J. Butler, to which reference is had for other detailedstructural characteristics of such repeaters; the parts here shown beingidentified by the reference numbers used for the identification of thecorresponding parts of the repeater of said patent. I

The system thus far described is representative of a large number offire alarm systems now in use by municipalities and various private andpublic institutions. All of the existing systems of the type representedare, however, as hereinbefore pointed out, utilizing direct current fortheir operation and, in most instances, the direct current is suppliedby storage batteries of which two sets are provided for each circuit,to. the end that the batteries for all bf the various circuits may besimultaneously charged without connecting thesource of charging currentto the sig naling lines and without establishing interconnectionsbetween such lines. Such avoidance of interconnections assures that anyone fault (such as an insulation break down to the ground or to aforeign circuit) will not impair the operability of more than thecircuit upon which it occurs, be that circuit a street or transmittingstation circuit, a local circuit, or the circuit from which chargingcurrent for the storage batteries is derived.

The provision of separate current sources is also of great importance inthat it enables the various street or transmitting station circuits andlocal circuit, or circuits to be temporarily connected in series witheach other in the event that it is necessary or desirable to temporarilysuspend the use of the automatic repeater (as for routine cleaning,lubrication, or emergency repairs). The purpose of such a. seriesconnection is to assure that, in the absence of grounds or crossesbetween circuits, the initiation of a signal at any transmitting stationwill cause such signal to be manifested by the receiving instruments ofthe local circuit or circuits and will react upon other transmittingstations in the same or other circuits substantially as if the repeaterwas in circuit. The purpose of reaction or socalled reflex actionbetween transmitting station circuits is to assure that, should themechanism of any transmitting stations be set in motion during theformulation of the signal of another station, or simultaneouslytherewith, there will be no interference or mutilation of signals butthe signals of the various transmitting stations will be manifested bythe receiving instruments at the receiving stations, one after an other,through the functioning of the so-called perfect non-interference andsuccession mechanism of the various transmitting stations, in a mannerwell understood by those skilled in this art.

Commercial forms of transmitting stations, of the perfectnon-interference and succession type hereinbefore referred to, havenot,heretofore been found to be suited for operation upon circuitsenergized by alternating instead of direct current; and the same is trueof automatic repeaters of commercial types such, for example, as thathereinbefore referred to. Pursuant, however, to this invention, thecircuits indicated may each be independently energized from one sourceof alternating current supply, through inductive coupling, as by thetransformers T, T, T, T, so

as to avoid establishing any connections between .said circuits such asmight permit a fault on one circuit to impair the operability ofanother. To this end, the connections to the windings 31, 31 of theelectromagnets of the repeater R, and of the corresponding windings ofthe electromagnets 311 of each of the transmitting stations TS and ofthe electromagnet 312 of the receiving instrument RS are arranged so asto provide two current paths in parallel. Rectifying means are includedin respective ones of said paths, said means being so connected that theapplication of an alternating electromotive force between the re-'spective connected ends of said paths will result in the flow ofeffective energizing current a1- ternately in one and the other of themagnet windings. Such rectifying means may be of any desired typearranged to act to facilitate current flow in one direction and toopposealmost to the point of complete suppressionfiow of current in theopposite direction. For convenience, the rectifying means of each of therespective paths will be termed a rectifying unit; and wherever thisterm is hereinafter used, it is intended to define a structure whichwill facilitate the flow therethrough of current in one direction andwill obstruct the flow of current therethrough in the oppositedirection, such, for example, as a unit comprising one or more copperoxide discs of such characteristics and so associated as to provideso-called asymmetric units.

The relative arrangement of windings and rectifying units, as indicatedin Fig. 1, is one which is particularly convenient both for illustrationand for application to the electromagnet windings of existinginstruments heretofore operated from direct current sources. As shown inconnection with the portion of the repeater R which is responsive tocircuits S one end of the winding 31 is connected to one end of thewinding 31, (as for direct current operation) and the remaining ends ofsaid windings are serially connected through the rectifying units ,f andg, which units are so relatively connected as to cooperate infacilitating a circulating current through said electromagnet windings.One of the line terminals is applied to said first named connection andthe other line terminal is applied to said last named connectionintermediate said rectifying units. As the connections shown for thewindings 31 and 31' associated with circuits S and S as well as thosefor the electromagnets 311 and 312 are identical with those of therepeater magnet windings 31 and 31' for circuit S a repetition of thedetailed description of same at this point is unnecessary. I

It should be understood that one end of the magnet core portion enclosedby one of the windings of any given magnet is connected to the adjacentend of the core portion enclosed by the other winding of such magnet, bythe usual ycke or strap so as to collectively form a conventionalU-shaped magnet, and that suitable armatures cooperate with the freepoles of respective ones of such magnets; but, in the interests ofclearness and simplicity, such strap or yoke portions of the magnetcores are omitted in Figs. 1, 2, 3 and 7, and the armatures are omittedother than in the representations of the transmitting stations of Fig.1.

The operation of the signaling system of Fig. 1 is as follows:

Assuming all parts to be in their normal positions and that a source ofalternating current supply is applied to the terminals providedtherefor, as indicated on the drawings,alternating current flow will beinduced in the various circuits S S S and L, through the transformers T,T, T, T, in a well known manner, thus supplying all of said circuitsfrom a single source while avoiding interconnecting current pathsbetween such circuits;

Inasmuch as the cut-outs C0 of the transmitting stations TS, TS, TS ofcircuits S S and S are in closed condition, substantially all of theline current will be shuntedaround the magnets 311 of said stations.Inasmuch as the effect of the current flow upon each of the othermagnets shown will be alike, it will be described in detail for but oneof said magnets. Considering, therefore, the eifect of the current flowin circuit S through the windings 31 and 31' of the electromagnet of therepeater R which is associated with said circuit:

During a given half cycle, substantially all of such current will flowthrough one or the other of the associated rectifying units, say, forexample, the unit 1 and its associated winding 31; and the remainder ofsuch current, if any, will pass through the other of the associatedrectifying units, say the unit g and its associated winding 31'. Suchcurrent as may, at any such time, flow through said winding 31,will tendto neutralize the effect of the current then flowing through theassociated winding 31; but, inasmuch as the action of said rectifyingunit g will serve during such half cycle to almost, if not completely,suppress current flow through said winding 31, the effect of suchadverse current flow. will be inappreciable, and said rectifying unit Iwill, throughout such half cycle, facilitate the flow of practically all(if not all) of said line current through the winding 31.

As the line current flow decays during the latter portion of such halfcycle, the inductive tendency toward persistence of current flow throughsaid winding 31 will result in the development of a flow of circulatingcurrent, say from one terminal of said winding 31, through the directconnection therewith of one end of said winding 31, thence through saidwinding 31' in such direction as to induce, in that limb of the magnetcore which is enclosed by said wind-' ing 31, a magnetomotive forcecooperative in direction to that induced in the other limb of said coreby the flow of line current through the coil 31 during the early portionof such half cycle, and from the other end of said winding 31', throughrectifying units g and f to the remaining end of said winding 31.

During the first portion of the next succeeding half cycle, therectifying unit g will correspondingly facilitate current flow throughthe winding 31' in such direction as to supplement the effect of currentflow during the first half cycle, and the fall of potential due to theimpedance presented to the line current flow by said winding31' and itsassociated rectifying unit y, will result in the complete termination ofappreciable current flow in the direction of the first deof current flowthrough said winding.

From the foregoing it will be observed that provision is made for themaintenance of a circulating current through the windings and rectifyingunits, suificient to prevent armature retraction during the subsidenceand suspension of line current flow in one direction and until linecurrent flow in the opposite direction has developed to an appreciableextent. It will also be noted that the arrangement is such that thecirculating current induced by the winding last energized appears to berapidly choked by the inductance of the other winding, so as to assurerapid demagnetization responsive to interruptions of the signalingcircuit.

In any event, it has been'found that electromagnets of signalinginstruments, when connected in an alternating current circuit asindicated by Fig. 1, will afiord dependable operability in response toseries of impulses having duration and interimpulse open circuitintervals as short as any to which the instruments were designed tooperate when connected in a direct current circuit, and with asubstantially corresponding factor of safety.

In the use of alternating currents of frequencies of from 25 to 60cycles, as ordinarily found in commercial distribution systems, it wouldappear that the density of the magnetic lines of force does not havetime to become uniform throughout the solid core of a U-shapedelectromagnet, the windings of which are connected as shown in Fig. 1.For example, at the time of maximum current flow through winding 31, theportion of said core enclosed by said winding has induced therein linesof force of a density exceeding that which is communicated therefrom tothe armature at the one end or through the strap or center of theU-shaped core to the other limb so that, at the time the current flowthrough the winding 31 is decreasing, during the second portion of thehalf cycle when current flow is in the direction facilitated byrectifying unit f, the magnetomotive force in the portion of the corewithin the winding 31 is still rising. While such a condition prevails,the electromotive force induced inthe winding 31 will oppose the flow ofcirculating current then induced in winding 31, due to the decay of thehalf wave current flow, and the resultant decrease in magnetization ofthe portion of the core enclosed by the winding 31. Ob-

viously, the action just described takes place in a corresponding mannerjust after each maximum current flow through the winding 31 so that,although the arrangement of rectifiers and cone nections here shownbrings'about an operating condition which minimizes vibration due topassing the zero point during reversals in direction of line currentflow, and thereby renders such vibration inappreciable, if at allpresent,--such arrangement also assures sufficiently promptdemagnetization to provide for correct response to signaling impulses atsufficiently rapid timing to meet the requirements of most classes ofsignaling.

In the event of the operation of the mechanism of one of thetransmitting stations TS, TS, TS,-

upon breaking of the shunt at C0, the magnet 311 v of the repeater Rassociated with circuit S The operation of the system, incident to theformulation of a signal at any oneof the stations TS will (aside fromdifference in manner of current flow through electromagnet windings, ashereinbefore described) be substantially the same as that incident tothe formulation of a signal in a municipal fire alarm system of acommonly used type, such as that shown in Fig. 1, and as such operationis well understood by those skilled in this art, a recital in thisspecification of the details of such operation seems unnecessary.

The arrangement of Fig. 2 is identical in func tional effect with thatindicated in Fig. 1, but its application to existing magnets cannotordinarily be accomplished with as great facility as that indicated byFig. 1. This is because the windings of U-shaped electromagnets arecustomarily connected through the free ends of the inner layers of therespective windings, and the free ends of the outer layers are used forthe respective line connections. Thus, in order to include a rectifyingunit in the connection between the inner layers of the respectivewindings, (as indicated in Fig. 2) it would be necessary to open thepreviously existing connection and to splice out both of thedisconnected ends, while the corresponding portion of the arrangementindicated by Fig. 1 may be obtained by merely splicing one conductor tothe previously connected free ends of the inner layers. Furthermore,there are certain types of magnets having but one spool for the winding,so that it is lilgely to be inconvenient to obtain separate access toends previously connected between desired divisions of the winding,although it may be that a connection can be readily applied to a portionof such a single winding substantially midway between the ends thereof,in 'which case the arrangement indicated by Fig. 1 can be applied withmuch greater facility.

Differently stated, it will be noted that, in the arrangement of Fig. 1,the rectifying unit g is situated in a position corresponding to that ofthe lead y of the winding 31 of Fig. 2; while in Fig. 2 the rectifyingunit g is situated in a position corresponding to that of the lead a: ofthe winding 31' of Fig. 1.

In order to more clearly disclose the relative directions of thewindings when connected as in Figs. 1 and 2, same are diagrammaticallyindicated in Fig. 4, in which it will be noted that two parallel pathsare provided from the line wire (1, one of which paths includes therectifying unit 1 which is so connected as to facilitate current flow 7from wire d, through winding 31 in counter-clockwise direction (lookingat the pole of the magnet 'to which this winding is applied), and thenceto wire e; while the other path is through conductor 11/, throughwinding 31' in a corresponding 31,-thus tending to induce amagnetomotive force; in such direction as to develop a plus or northpolarity at the free pole of the limb of the magnet core to which thewinding 31 is applied and to develop a minus or south polarity at thefree pole of the limb of the magnet core to which the winding 31 isapplied. As such potential between wires 11 and e decreases, during thelatter part of the half wave, a circulating current may persist from thewinding 31, through the rectifying unit g, the winding 31, the conductor3 and the rectifying unit I, such as will assist in retaining thearmature in attracted position while the electromotive force betweenconductors d 'and e passes zero.

correspondingly, when electromotive force is building up in thedirection to cause current flow from wire e toward wire d, substantiallyall of the resultant current flow will be through rectifying unit g andwinding 31, and hence in a direction tending a develop a minus or southpole at the free end of the limb of the core to which said winding isapplied; such current fiow being in a direction to cooperate with thatinduced by the decay of the current flow through winding 31 and themagnetomotive force induced thereby being in the same direction as thatinduced by the current flow through the winding 31 during the precedinghalf cycle. ance of said winding 31 will cooperate with the rectifyingunit I in opposing current flow therethrough in such direction as wouldtend to impair the building up of magnetism in the magnet coreresponsive to current flow through the winding 31'.

It will be noted that, with arrangements such as those herev shown, itis unnecessary to provide rectifying units suited for withstanding thetotal electromotive force of the line current source, but it willsuflice if such units are suited for withstanding the maximum fall ofpotential which is developed across the windings with which they are tocooperate. In any event, however, each unit should be such as todependably withstand the .fall of potential developed at full linecurrent strength across the other associated rectifying unit and thewinding in the current path parallel therewith. If provision should bemade for comparatively high speed operation, the characteristics of eachof the parallel current paths should be correspondingly altered.

For example, using a commercial form of copper oxide disc in each of therectifying units, and with a given electromagnet and an associatedarmature with fixed operating load, it has been found that movement ofthe armature from retracted to attracted position can be as dependablyeifected by the use of two copper oxide discs per rectifier unit as bythe use of any greater number, and the energy absorption in aconstantcurrent series circuit, when using two discs per unit is on theorder of 0.5 volt-amperes, as compared with 1.15 volt-amperes whenemploying discs per unit. If, however, it is required that the armatureof the electromagnet shall be de pendably responsive to circuit closuresno longer than 0.048 seconds, it will become necessary to so increasethe line current that the energy absorption of the magnet and itsassociated units will be on the order of not less than 1.25volt-amperes, for any number of discs used, from two to ten; and willonly increase to a value on the order of 1.6 volt-amperes if 15 discsper unit are employed. With same magnet and armature, with breaks of0.048 second and closures of like duration, the permissible increase inline current strengths at which dependable drop-away would occur, abovethat causing absorption of 1.25 voltamperes, has been found to be suchas to result in energy absorption by the associated windings and units,as follows: for five discs per unit, 2.5

Furthermore, the inductvolt-amperes; for six discs per unit, 3.625voltamperes; for seven discs per unit, 4.7 volt-amperes; for eight discsper unit, more than 5.25 volt-amperes. Furthermore, if it is requiredthat the armature of the electromagnet shall respond to both breaks aswell as closures which areas short as 0.033 seconds, dependable servicewill require the use of eight discs per circuit and, if the line currentstrength is subject to considerable variation, the use of a largernumber of discs will be desirable. For example, using the same magnetand armature, it was found that with ten discs per unit the armaturewould be dependably moved from retracted to attracted position duringclosures of 0.033 seconds at line current strength such as would resultin absorption by the magnet and its associated units of not less than1.35 voltamperes, while drop away of the armature could not bedependably obtained when the line current was so increased that suchenergy absorption exceeded 1.6 volt-amperes; while, with fifteen discsper unit, line current strengths such as would cause absorption of 1.625volt-amperes or more would assure attractive movement of the armatureduring closures of 0.033 seconds and failures to retract during breaksof like length would not occur at any line current strength causingabsorption of not more than 2.75 voltamperes.

Under certain operating conditions, it has been found to be desirable tominimize, as far as practicable, both the energy absorption of eachwinding and its associated rectifying units;and, under other conditions,to minimize the required operating current strength for a given magnetwinding, irrespective of savings in energy absorption. For example, ifit is proposed to change the current supply source of a given signalingcircuit from direct to alternating current, and such circuit includes anumber of electromagnets f and their associated rectifying units sogreat that the alternating current energy absorption thereof will be asubstantial proportion of that of the entire circuit, then the questionof the amount of energy absorbed by each winding and its associatedrectifying units becomes a primeconsideration if the total energyabsorption for the circuit must be limited.

On the other hand, if a corresponding change is to be made in a circuitof which the impedance provided by resistance of line wire is a far moreimportant factor than that resulting from the inclusion of the requirednumber of electromagnets and'their associated rectifying units, it maybecome of prime importance to minimize, as far as practicable, the linecurrent required to obtain dependable operation, even if the energyabsorption for the magnets and their associated rectifyin'g units is notcorrespondingly decreased, on account of the savingof energy absorptionwhich will result from minimizingv of line current strength, because ofthe preponderance of the resistance of the line wire and cableconductors in the total line impedance. To provide for the latter classof cases, the arrangement shown by Figs. 3 and 5 may be substituted forthat shown by Figs. 2 and 4. .The difference between the arrangement ofFigs. 2 and 4 and that of Figs. 3 and 5 is, as will be most clearly seenby Fig. 5, the provision of the conductor h which connects the currentpath through the rectifying unit 3 and the winding 31, at a. pointbetween said unit and said winding, with a corresponding point in theparallel current path through the winding 31' and unit 9. I

By such use of the conductor h, it has been found that movement of thearmature from retracted to attracted position can be as depend-.-

ably obtained with an energy absorption of 0.25

0.15 volt-amperes using two discs to about 0.025

volt-amperes using fifteen discs. It has been found, however, that asthe line current is increased, the characteristics of rectifiersconnected in accordance with Figs. 3 and 5 must be revised undercircumstances such as would not require revision if connected inaccordance with Figs. 2 and 4.

- For example, in the use of rectifying units composed of a commercialform of copper oxide discs, it has been found that, with a given magnetconnected in a signaling system such as that indicated by Fig. 1,although a line current strength such as would cause an energyabsorption of 0.25 volt-amperes in. the magnet and its associatedrectifiers would cause the armature to move from retracted to attracted,using one disc per'unit, and with an energy absorption on the order of0.32 volt-amperes using two discs-if the line current strength is soincreased as to correspondingly result in an absorption of energy to theextent of 0.85 volt-amperes dependable operation will require at leasttwo, and pref erably three discs per unit; although if the conductor hof Figs. 3 and 5 is not used, thedependability of operation will not beimpaired as the line current is increased so as to cause energyabsorption from a minimum on the order of 0.5 volt-amperes to a maximumof nearly 2.0 volt-amperes.

It seemsprobable that the ability thus indicated of the arrangementwithout the conductor h to dependably operate with fewer discs than thatwith the conductor h, is because of the lack, in the arrangement withsaid conductor, of the inductive effect of the windings which, in theabsence of the conductor h, tends to decrease strain upon therectifiers; but which does not so protect the rectifiers when thisconductor is used. correspondingly, a given speed of operation requiresa different circuit condition if the conductor h is used. For example,if the conductor h is used in connection with rectifying units composedof the commercial form of copper oxide discs hereinbefore referred to,re-

sponse to signal formulation using a series of closures and breaks asshort as 0.048 seconds, requires, for dependable pick-up and drop awayof the armature, a line current strength which will result in energyabsorption per magnet and its associated rectifying units not less thanthe lower and not higher than the highest of the following volt-amperevalues: For three discs, 0.77, to 1.3; for four discs, 0.9 to 1.6; forfive discs, 1.0 to 2.3; for six discs, 1.2 to 2.3; for seven discs, 1.13to 2175. If the minimum periods of closure and break are reduced to0.033 seconds, other conditions remaining the same, dependable operationhas been found to require at least nine discs, and with ten discs theline current strength must be such as will cause an energy absorption ofat least 1.45 and not to exceed 1.5 volt-amperes; while with twelvediscs it may not be less than 1.75 or more than 1.85, while for fifteendiscs, it may not be less than 2.0 or more than 2.65 volt-amperes.

Considered nowfrom the standpoint of required operating current, it hasbeen found that the use of the conductor h effects an economy on theorder of 30% in current required to pick up on closures. of a givenduration.

The relative operating characteristics of a given magnet when subjectedto closures and breaks of like duration, with and without the conductorh, is further illustrated in Fig. 6,in which the line A isrepresentative of the breaks and closures of the exciting circuit, thecurve B is representative of the changes in the magnetomotive force ifthe conductor h is not used, while curve C is representative of themagnetomotive force if the conductor h is used. It will be here noted byreference to curve B, that, without the conductor h, the flux decreasesduring breaks, to an extent which brings it down almost to the strengtheffective before the first circuit closure of the series, and risesduring each closure to substantially maximum strength. With conductor hin use, the increases in the flux, as represented by curve C, aresomewhat cumulative, while the decreases during breaks lack more andmore, following succeeding closures, from returning to the strengtheffective before the first closure of the series. The discrepancies bothas to quickness in attaining full energization and quickness indeenergization when the conductor 71. is used may doubtless be traced,in large part, to the fact that, when the conductor h is used, there isan independent path for the circulating current in each of the separatewindings while, without the conductor h, all circulating current musttraverse both windings.

When attempts have heretofore been made to utilize alternating currentfor the excitation of the controlling magnets of signaling instrumentsin a series circuit, one of the serious difficulties encountered hasarisen because the armatures of some of thesignaling instruments do notrespond to circuit closures as quickly as those of other instruments,and, when those most quickly acting have moved in response to theexcitation of their associated magnet windings, the resultant change inimpedance has caused a substantial decrease in line current strength sothat, if a reasonable factor of safety was to be maintained for theslower acting instruments, it has been necessary to either provide anelectromotive force such as would cause an objectionably large currentflow prior to the movement of the armatures from retracted position orelse to add such an amount of non-inductive resistance to each circuitthat the aggregate of the impedance of all of the magnets includedtherein will represent but a minor portion of that of the entirecircuit; thus correspondingly requiring the use of an electromotiveforce greatly in excess of what would otherwise be needful,or, ifpractical conditions require that the total electromotive force percircuit shall fall within certain limits, requiring distribution betweena plurality of circuits, of the magnets which could otherwise have beenincluded in one circuit. Obviously, all such expedients areobjectionable for a variety of reasons.

Ina signaling system having circuits in which the magnet windings -areco-related with rectifying units in. the manner hereinbefore 'describedand as indicated in the accompanying drawings, it will be foundthat theimpedance offered to flow of current in the circuit, at any givenstrength, by the windings of any given magnet and its associatedrectifying units, will not change to an objectionable extent, andusually not to an appreciable extent, upon movement of the associatedarmature from retracted to attracted position.

For example, in a circuit supplied with energy from a constant potentialtransformer and serially including the electromagnet windings and theassociated rectifying units of such type and number of instruments thatthe impedance thereof will be several times that of comparativelynoninductive circuit components (such as line wire) ,-the line currentstrength will not become appreciably impaired because of the movementsof the armatures of instruments most quickly responsive to circuitclosures, thereby assuring maintenance of a current flow of adequatestrength to cause the armatures of all of the instruments to move toattracted position.

The description of various embodiments of this invention has, up to thepresent point, been particularly directed to forms thereof in which fullWave rectification is effected, as such rectification is usuallydeemed'far preferable, if readily obtainable, for effecting theenergization of electromagnets of signaling systems such, for example,as that indicated by Fig. -l. Inasmuch, however, as the broader aspectsof this invention render its utilization advantageous in classes ofservice where half wave rectification accomplished in accordance withthis invention will give entirely satisfactory results, it is pointedout that such rectification may be effected pursuant to this inventionby merely connecting a rectifying unit having suitable characteristics(as hereinbef'ore more fully explained) in parallel with the winding ofeach electro-magnet.

For example, referring to the arrangement shown by Fig. 5,the winding31' and the rectifying unit 1 could be omitted, so that there would betwo current paths between conductor d and conductor e, which paths wouldbe connected in parallel at the ends thereof, one path including thewinding 31 (or, if desired, both the windings 31 and 31' in series) andthe other current path including one rectifying unit as, for example,the unit g. In Fig. '7, electromagnets are shown arranged as justindicated.

When a circuit is. arranged for half wave rectification, as justindicated, if a substantial portion of the total circuit impedance isthat of the included electromagnets and their associated reetifiers, itis desirable that substantially onehalf of the magnets shall beconnected to use onehalf of the wave and the remainder of the magnets toutilize the other half of the wave. In any event, rectifying uriitsemployed in accordance with this invention are not at any time subjectedto an electromotive force exceeding that resultant from the impedance ofthe electromagnet winding in parallel therewith; each winding,considered by itself,-is subjected to half wave energizationsupplemented by the flow of a circulating current through a current pathsuch as to tend to maintain the magnetcmotive force throughout theintervals between half wave impulses imparted by the exciting'circuitand which circulating current path has such characteristics as toprevent continuation of such circulating' current for a time so great asto unduly retard the demagnetization of the core follow- &

- during each half wave of all cycles, one or the other of such pathswill be independently available.

1 Fig. 7 shows a circuit'such as might be utilized for connecting thebells and registers used for manifesting alarms in fire houses connectedby ,a circuit such as the circuit L in Fig. 1; the

tower bell striker at receiving station RS being connected in thecircuit as shown in Fig. 1, but the receiving instruments represented asbeing at the various fire houses FH, FH, etc., are arranged so that therectifiers j cause their associated electromagnet 31 at part of suchinstru- 'ments to be energized by a given half-wave and the rectifiers gcorrespondingly cause their associated electromagnets 31 at theremaining instruments to be energized by the succeeding halfwave.

From the foregoing it will be apparent that types of signaling apparatuswhich are at present commercially available, and which are suited foroperation in direct current circuits, may be adapted for use inalternating current circuits without change in the physicalcharacteristics of the electromagn'ets and without any such change inimpedance or in the energy required for their effective excitation as torender them unsuited to uses corresponding to those to which they haveheretofore been put. Thus, for example, in the case of a signalingsystem such as that of Fig. 1, the circuits S S S and L may be suppliedfrom a single alternating current source. If the use of storagebatteries is desired, but one battery will be needed which, operating inany well known manner, as through a suitable motor generator, willsupply the needed alternating current for the excitation of thetransformers T, T, T, T; a, duplicate battery not being needed as suchbattery could be floated or chargedrwhile being discharged withoutinterconnecting the signaling circuits or exposing them to connectionwith any foreign circuit, to the end that no current path would beestablished between the circuits notwithstanding their ultimatedependence, at any given time, upon a single storage battery.

The avoidance of using individual transformers in connection with eachof the various electromagnets as well as the avoidance of the lossesincident to the use of .four rectifying units (connected in bridgeinstead of two, in association with each of the line magnets)contributes materially in rendering it possible to utilize alternatingcurrent for the supply of circuits such as S S and S in which thenon-interference magnets 311 of the various transmitting stations arenormally shunted by their respectively associated cut-outs CO, so thatit is important that the line current strength shall not be undulydiminished by the inclusion of any required number of such magnets intheir circuit. The importance of this feature is better understood whenit is recalled that, in the case of a fire alarm system such as thatindicated by Fig. 1, the sudden bursting forth of a spectacular fire mayresult in the mechanism of numerous transmitting stations being set inmotion at or about the same time, with a resultant inclusion of theimpedance of many non-interference magnets in a series line circuit.Obviously, if the cumulative effect of the insertion of such impedancesis to decrease the line current to a strength below that at which theautomatic repeater or other receiving instruments will respond, or belowthat at which the armatures of the non-interference magnets will be heldduring signal formulation of their associated stations the signal forsuch fire may be completely lost. f

It is believed that, with the foregoing explanations, the operation ofthis invention will be fully understood by those skilled in this art,and a further detailed recital thereof will, therefore, be omitted.

Although, in a more specific sense, this invention relates to emergencysignaling and communication systems employing series circuits such, forexample, as those indicated in Fig. 1; the broader features of thisinvention are not limited to the specific embodiments thereof which areshown in the annexed drawings and are described in detail in theforegoing specification, but are suited for use under practically everycondition in which it is desirable to efiect the excitation of anelectromagnet by the use of alternating current.

.What I therefore claim and desire to secure by Letters Patent of theUnited States of America is:

1. An electromagnetically controlled instrument including a U-shapedmagnet with windings on the respective limbs thereof, an end of one ofsaid windings connected to such a one of the ends of the other thatcurrent flow through said windings from one to the other of theremaining ends thereof will effect intended magnetization; incombination with .an interconnection between said remaining ends,rectifying means serially included in said interconnection, saidrectifying means substantially opposing current flow toward one, andaway from the other of said remaining ends, and energizing current tapsapplied to saidinterwinding connection and between the terminals of saidrectifying means.

2. A signaling instrument including a magnet winding and its associatedcore in' combination with rectifying means having extreme terminals andan intermediate mrminal, connections providing a closed loop seriallyincluding said winding and said means whereby the circulation of currentin said loop will induce a magnetomotive force in said core and saidmeans will oppose flow 1n one direction of a circulating current throughsaid loop, an energizing alternating current tap applied to said loopintermediate the ends of said winding, and a second alternating currenttap applied to said loop intermediate the extreme terminals of saidmeans.

3. A signaling instrument including an electromagnet having twowindings, connections pr oviding a closed loop serially including saidwindings, rectifying means" serially included in said connections tooppose current flow in said loop in a given direction, an energizingcurrent tap applied to said loop between a terminal of one winding andthe rectifying means of one of said and the rectifying means of one ofsaid connections, a second energizing current tap applied to saidloopbetween a terminal of the other windnetic path with two windingscumulatively act'- ing and the rectifying means of the other of saidconnections, and an interconnection between the remaining ends of saidwindings.

5. In an electric current rectifying system adapted for supplyingrectified current directly from a source of alternating current, thecombination comprising an electro-magnet having a winding split into twoparts conductively connected together, a circuit including a half-waverectifying device connected to energize one part of said winding andhaving conducting connections with said source, and a second circuithaving a conductor in common with the first circuit and a secondhalf-wave rectifying device disposed to have opposite polarity to thefirst, said second circuit-being connected to energize the other part ofsaid winding and conductively connected to said source.

6. In an electric current rectifying system adapted for supplyingrectified current from a source of alternating current, a supplycircuit, an electro-magnet having a single magnetic path with twowindings cumulatively acting upon said path and conductively connectedin and serially related to said circuit in parallel branches to'eachother to form a closed loop, and a'rectifier in each branch, saidrectifiers being in cooperative relation within said loop,

7. In an electric current rectifying system adapted for supplyingrectified current from a source of alternating current, a supplycircuit, an electro-magnet having a single magnetic path with twowindings cumulatively acting'upon said path, each winding beingconductively connected in and serially related to said circuit and inparallel relation each to the other, rectifying means associated withone winding to oppose current flow in a certain direction therethroughwith re? lation to said source, and rectifying means associated with theother winding to oppose current fiow in the opposite directiontherethrough.

8. In an electric current rectifying system adapted for supplyingrectified current to an electro-magnet directly from a source ofalternating current, a magnet having a single maging thereupon, analternating current supply circuit serially connecting said windings insuch a manner that parallel'current paths are provided through the twowindings, a rectifying unit connected to a terminal of one winding tooppose current flow in a certain direction therethrough,

and a rectifying unit connected to a terminal of' v the other winding tooppose current fiow there,-

through other than in a direction to cooperate" with unopposed currentfiow in the first named 9. A device of the character describedcomprising, in combination, a pair of altemating said leads, and arectifier in each coil circuit,

said rectifiers being in opposed relation so as to permit fiow ofcurrent in the respective coils during opposite alternations in the linecurrent.

'10. A device of the character described comprising, in combination withalternating current leads, duplicate magnet coils wound on a common corefor cumulative action thereupon and oppositely connected in said leads,and a rectifier in each coil circuit, said rectifiers being in opposedrelation so as to permit flow of current in the respective coils duringopposite altemations of the line current.

11. A device of the character described comprising, in combination withalternating current leads, duplicate magnet coils wound on a common corefor cumulative action thereupon and oppositely connected in said leads,a rectifier in each coil circuit, said rectifiers being in opposedrelation so as to permit fiow of current in the respective coils duringopposite alternations of the nating current voltage.

12. In an electric current rectifying system half-wave rectifying deviceconnected to energize one winding portion of said electro-magnet, saidcircuit being conductively connected to said source, a second circuithaving a rectifying device connected in series therewith conductivelyconnected to energize a second portion of the windings of saidelectro-magnet, conductively connected to said source, and having apolarity with respect to the first rectifying device such that themagneto motive force in said portions is the same,

said first and second circuits having a portion in common.

13. In an electric current rectifying system adapted for supplyingrectified current directly from a source of alternating current, thecombination comprising an electro-magnet having a single magnetic path,a winding provided with two end terminals and a mid-point terminal, a

conductor having iii series therewith a half-wave rectifying deviceconnected to one of said end terminals, a second conductor having asecond half-wave rectifying device in series therewith connected to theother end terminal, and arranged to have a polarity opposite to thefirst, a third conductor connecting together the free poles of saidrectifying devices and adapted to be connected to one side of thealternating current sourceof supply, and a fourth conductor connected tosaid mid-point terminal and adapted to be connected with the other sideof said alternating current source. 7

i r C. E. BEACH.

